A liquid crystal display device has such an advantage, compared with other display devices, that the dimension of the depth (thickness) can be made significantly thinner, power consumption is low, and a full-color image can be obtained with ease, and therefore has been applied in a wide variety of fields in recent years. The liquid crystal display device generally has a structure wherein a liquid crystal layer is sandwiched between a pair of glass substrates.
With respect to the glass substrates, a transparent conductive layer, an organic high polymer film, and a thin film such as a metallic film are deposited, and by patterning of these films, switching elements such as TFT (Thin Film Transistors) and wiring for driving and controlling the switching elements are formed.
In the process of forming such films, it is required to remove particles of submicrons to several microns adhering on the glass substrates by cleaning the substrates. This is because when the thin films are formed while the particles still remain on the glass substrates, wiring defect such as breakage and leaking of wire occurs in the wiring formed by patterning the thin films. The wiring defect induces malfunctioning of the switching elements, which might cause a line defect or dot defect in the product liquid crystal display device. The same problem is also presented in manufacturing of ICs and LSIs.
In order to solve this problem, it has been a common practice to remove the particles on the substrates by cleaning the substrates such as glass substrates in a cleaning apparatus, and thereafter deposit thin films on the substrates. As such a cleaning apparatus, a cleaning apparatus of the overflow system is available, in which a cleaning liquid flows into a cleaning tank substantially uniformly. A cleaning apparatus 100 as shown in FIG. 7 is an example of such a cleaning apparatus, which includes at least a pump 101, a filter 102, a cleaning tank 103, an inflow opening 105, releasing means 106, and a punching plate 107.
In this cleaning apparatus 100, first, the particles contained in the cleaning liquid which has been forced out by the pump 101 are removed by the filter 102. The cleaning liquid from which the particles are removed flows into the cleaning tank 103 through the inflow opening 105 provided in a flat manner on a bottom surface of the cleaning tank 103. Above the inflow opening 105 is provided the punching plate 107 which smooths the flow of the cleaning liquid, and as a result the cleaning liquid flows into the cleaning tank 103 uniformly.
In the cleaning tank 103, a plurality of substrates 104 (for example, glass substrates) are placed as a cleaning target, and the substrates 104 are cleaned by the cleaning liquid flowing uniformly. The cleaning liquid is released by the releasing means 106 through outflow openings (not shown) provided on the cleaning tank 103.
As described, the inflow opening 105 is provided in a flat manner on the bottom surface of the cleaning tank 103, and since the punching plate 107 is provided, as shown in FIG. 8, the cleaning liquid flows into the cleaning tank 103 uniformly. The cleaning liquid then flows from the lower portion of the cleaning tank 103 towards the upper portion where two outflow openings 108 are provided. The substrates 104 are cleaned by this flow of the cleaning liquid. Thereafter, as described above, the cleaning liquid flows out from the outflow openings 108 provided so as to contact the upper ends of the cleaning tank 103, and is released by the releasing means 106.
As the cleaning apparatus of the overflow system, other than the cleaning apparatus 100 as described above, the following cleaning apparatuses are available. In a cleaning apparatus 110, as shown in FIG. 9, the cleaning liquid flows in the form of radial distribution into a cleaning tank 113 from inflow openings 115 provided in a flat manner on the bottom surface of the cleaning tank 113. The cleaning liquid flowing in this manner cleans the substrates 104 and then flows out from two outflow openings 118 provided on the side surfaces of the cleaning tank 113, contacting the upper surface.
In a cleaning apparatus 120, as shown in FIG. 10, flat inflow openings 125 are provided on the upper surface of a cleaning tank 123, and the cleaning liquid flows in uniformly from the inflow openings 125. The cleaning liquid flowing in this manner cleans the substrates 104 and then flows out from two outflow openings 128 provided on the side surfaces of the cleaning tank 123 so as to contact the bottom surface.
Also, a cleaning apparatus in which a cleaning liquid which has flown into the cleaning apparatus flows out from a plurality of inflow openings is available. Namely, in this cleaning apparatus, the arrangement of the inflow openings and the outflow openings is opposite to that of the cleaning apparatus of the overflow system. For example, as shown in FIG. 11, in a cleaning apparatus 130, the cleaning liquid flows in from inflow openings 135 provided on the side surfaces of a cleaning tank 133, contracting the upper surface. The cleaning liquid flowing in this manner cleans the substrates 104 and then uniformly flows out from flat outflow openings 138 provided on the bottom surface of the cleaning tank 133.
As such a cleaning apparatus of the uniform flow system, especially as a cleaning apparatus for cleaning a silicon wafer which is a circular substrate used for ICs and LSIs, for example, as shown in FIG. 12, a cleaning apparatus 140 including a cleaning tank 143 having a cross section of substantially semi-circular shape is available.
In this cleaning apparatus 140, the shape of the cleaning tank 143 is set in accordance with the shape of a silicon wafer 144 provided as a cleaning target. On the upper portion of the cleaning tank 143, there is provided a pure water supplying section 142 for supplying pure water (cleaning liquid), and inside the cleaning tank 143 are provided a plurality of shower pipes for spraying pure water onto a position corresponding to the shape of the silicon wafer 144. Spraying of pure water by the shower pipes stirs the pure water in the cleaning tank 143, and the particles on the silicon wafer 144 are removed. Thereafter, the pure water is uniformly flown out from outflow openings 148 so as to be released.
As another example of the cleaning apparatus having the described arrangement, a cleaning apparatus as disclosed in Japanese Unexamined Patent publication No. 290134/1996 (Tokukaihei 8-290134) is available. In this cleaning apparatus 150, as shown in FIG. 13, two inflow openings 155 are provided on the upper end of one of the side surfaces of a cleaning tank 153 having substantially a rectangular parallelopiped shape so that the inflow angles of the pure water (cleaning liquid) are different. The flows of the pure water flown from the two inflow openings 155 remove the particles on the silicon wafer 144 (cleaning target), and thereafter merge into a single flow in the vicinity of flat outflow openings 158 provided on the bottom surface of the cleaning tank 153, thus cancelling out the flows. The pure water in which the flows have been cancelled out in this manner flows out through the outflow openings 158 so as to be released.
Meanwhile, a cleaning apparatus of the tornado system in which the cleaning liquid flown in from a plurality of inflow openings flows out from a single or plurality of outflow openings is known. As such a cleaning apparatus of the tornado system, for example, a cleaning apparatus 160 as shown in FIG. 14 is available, in which two inflow openings 165 are provided on the side surfaces of a cleaning tank 163 so as to contact the upper surface, and a single outflow opening 168 is provided so as to contact the bottom surface of the cleaning tank 163. In this cleaning apparatus 160, the substrates 104 are cleaned by the swirl formed by the cleaning liquid flown into the cleaning tank 163 from the two inflow openings 165, and the cleaning liquid flows out from the outflow opening 168 so as to be released.
Also, a cleaning apparatus as shown in FIG. 15 is available, in which two inflow openings 175 are provided on the side surfaces contacting the upper surface of a cleaning tank 173, and two outflow openings 178 are provided on the side surfaces contacting the bottom surface of the cleaning tank 173. In the cleaning apparatus 170, the substrates 104 are also cleaned by the swirl formed by the flows of the cleaning liquid in the cleaning tank 173.
The above cleaning apparatuses clean the substrates 104 in the described manners and the particles adhering on the substrates 104 are removed.
However, in the cleaning apparatus 100 of the overflow system, the cleaning liquid uniformly flowing in from the inflow openings 105 faces the viscous resistance by the substrates 104 (cleaning target). As a result, the flows of the cleaning liquid diverge towards the sides where the two outflow openings 108 are provided in their way up towards the upper portion of the cleaning tank 103. Thus, at the central portion of the cleaning tank 103 in the vicinity of the fluid surface where the cleaning liquid diverges, stagnation of the cleaning liquid is generated, and the particles reside in the stagnation thus generated (generation of residual particles).
When residual particles are generated in this manner, large numbers of particles remain particularly in a region on the substrates 104 placed in the cleaning tank 103, corresponding to the stagnated portion. Thus, on the substrates 104, two regions of (A) a contaminated region in which a large number of particles remain and contamination due to the particles is present and (B) a clean region in which the number of residual particles is less than a predetermined number are formed. As a result, nonuniformity in the number of residual particles is generated on the substrates 104.
Therefore, in order to evenly clean the substrates 104 with respect to the entire surfaces by the cleaning apparatus 100, it is required to continue cleaning until the number of residual particles in the contaminated region substantially equals the number of residual particles in the clean region. For this reason, it takes a long time to clean the entire surfaces of the substrates 104.
Further, another problem is presented that when taking the glass substrates 104 out of the cleaning tank 103 after cleaning, the particles remaining in the stagnation of the cleaning liquid adhere again onto the cleaned substrates 104, and the substrates 104 are re-contaminated.
In the cleaning apparatus 110, since the flows of the cleaning liquid are distributed radially, the amount of the cleaning liquid flowing towards the central portion in the vicinity of the fluid surface is large in the cleaning tank 113. Therefore, even though the residual particles are prevented from generating at the central portion to some degree, it is impossible to completely prevent generation of residual particles, and the above problems remain unsolved.
Likewise, in the cleaning apparatus of the overflow system such as the cleaning apparatus 120 in which the cleaning liquid flows uniformly into the cleaning tank 123 from above, the cleaning liquid diverges towards the sides on the lower portion of the cleaning tank 123 where the two outflow openings 128 are provided. Thus, the cleaning liquid stagnates where the cleaning liquid diverges, and the generation of residual particles cannot be prevented.
Also, in the cleaning apparatus 130 of the uniform outflow system, the flows of the cleaning liquid from the two inflow openings 135 form a large swirl in the cleaning tank 133. When the cleaning liquid forms a swirl in this manner, the flows of the cleaning liquid are weakened. Thus, in the cleaning apparatus 130, unlike the cleaning apparatus of the overflow system, no stagnation of the cleaning liquid is formed in the cleaning tank 133. However, since the flows of the cleaning liquid are weak, the particles on the substrates 104 cannot be removed effectively, and it takes a long time to clean the entire surfaces of the substrates 104.
In the cleaning apparatus 140 having the same arrangement as that of the cleaning apparatus 130, pure water is supplied from the upper portion of the cleaning tank 143, and the pure water is sprayed on the periphery of the silicon wafer 144 at the central portion of the cleaning tank 143. Thus, although the silicon wafer 144 is cleaned sufficiently, because the pure water is stirred in the central portion of the cleaning tank 143, the particles removed by cleaning are not released immediately from the outflow openings 148 and remain in the cleaning tank 143.
Also, in the cleaning apparatus 150 as disclosed in Japanese Unexamined Patent publication No. 290134/1996 (Tokukaihei 8-290134), the flows of pure water are cancelled out in the vicinity of the outflow openings 158. Thus, the particles removed do not remain in the cleaning tank 158 and are immediately released from the outflow openings 158, solving the problem of the cleaning apparatus 140. However, as shown in FIG. 13, by the pure water flowing in from the two inflow openings 155, stagnation is generated in a region as indicated by the arrow A in the upper portion of the cleaning tank 153.
In the cleaning apparatus 150, because the silicon wafer 144 used as a cleaning target is not as large as a glass substrate used for liquid crystal display devices, the effect of stagnation on cleaning is not as significant. However, when the size of the cleaning target is increased as large as the glass substrate, as in the cleaning apparatus of the overflow system, residual particles are generated by stagnation, and the cleaning effect is lowered significantly.
In the cleaning apparatuses 160 and 170, as in the cleaning apparatus 130, since the flows of the cleaning liquid form a large swirl, stagnation of the cleaning liquid is prevented in the cleaning tanks 163 and 173. However, the flows of the cleaning liquid forming a large swirl are not sufficient for cleaning the substrates 104, and the particles on the substrates 104 are not removed efficiently.
Also, as the inflow openings of the described cleaning apparatuses, a nozzle having opening sections has been adopted widely. However, almost no consideration had been given to the shape of the nozzle and the inflow amount of the cleaning liquid for allowing the particles to be removed most efficiently in the shortest period of time.